Downregulation of hypocretin/orexin after H1N1 Pandemrix vaccination of adolescent mice

Narcolepsy type 1 (NT1), characterized by the loss of hypocretin/orexin (HCRT) production in the lateral hypothalamus, has been linked to Pandemrix vaccination during the 2009 H1N1 pandemic, especially in children and adolescents. It is still unknown why this vaccination increased the risk of developing NT1. This study investigated the effects of Pandemrix vaccination during adolescence on Hcrt mRNA expression in mice. Mice received a primary vaccination (50 µL i.m.) during prepubescence and a booster vaccination during peri-adolescence. Hcrt expression was measured at three-time points after the vaccinations. Control groups included both a saline group and an undisturbed group of mice. Hcrt expression was decreased after both Pandemrix and saline injections, but 21 days after the second injection, the saline group no longer showed decreased Hcrt expression, while the Pandemrix group still exhibited a significant reduction of about 60% compared to the undisturbed control group. This finding suggests that Pandemrix vaccination during adolescence influences Hcrt expression in mice into early adulthood. The Hcrt mRNA level did not reach the low levels known to induce NT1 symptoms, instead, our finding supports the multiple-hit hypothesis of NT1 that states that several insults to the HCRT system may be needed to induce NT1 and that Pandemrix could be one such insult.

Experimental sickness reduces hypocretin receptor 1 expression in the lateral hypothalamus and ventral tegmental area of female mice

Recent studies have focused on how sickness behaviours, including lethargy, are coordinated in the brain in response to peripheral infections. Decreased hypocretin (orexin) signalling is associated with lethargy and previous research suggests that hypocretin signalling is downregulated during sickness. However, there are studies that find increases or no change in hypocretin signalling during sickness. It is further unknown whether hypocretin receptor expression changes during sickness. Using lipopolysaccharide (LPS) to induce sickness in female mice, we investigated how LPS-injection affects gene expression of hypocretin receptors and prepro-hypocretin as well as hypocretin-1 peptide concentrations in brain tissue. We found that hypocretin receptor 1 gene expression was downregulated during sickness in the lateral hypothalamus and ventral tegmental area, but not in the dorsal raphe nucleus or locus coeruleus. We found no changes in hypocretin receptor 2 expression. Using a gene expression calculation that accounts for primer efficiencies and multiple endogenous controls, we were unable to detect changes in prepro-hypocretin expression. Using radioimmunoassay, we found no change in hypocretin-1 peptide in rostral brain tissue. Our results indicate that hypocretin receptor expression can fluctuate during sickness, adding an additional level of complexity to understanding hypocretin signalling during sickness.

Repeated polysomnography and multiple sleep latency test in narcolepsy type 1 and other hypersomnolence disorders

BACKGROUND

The diagnosis of narcolepsy is based on clinical information, combined with polysomnography (PSG) and the Multiple Sleep Latency Test (MSLT). PSG and the MSLT are moderately reliable at diagnosing narcolepsy type 1 (NT1) but unreliable for diagnosing narcolepsy type 2 (NT2). This is a problem, especially given the increased risk of a false-positive MSLT in the context of circadian misalignment or sleep deprivation, both of which commonly occur in the general population.

AIM

We aimed to clarify the accuracy of PSG/MSLT testing in diagnosing NT1 versus controls without sleep disorders. Repeatability and reliability of PSG/MSLT testing and temporal changes in clinical findings of patients with NT1 versus patients with hypersomnolence with normal hypocretin-1 were compared.

METHOD

84 patients with NT1 and 100 patients with non-NT1-hypersomnolence disorders, all with congruent cerebrospinal fluid hypocretin-1 (CSF-hcrt-1) levels, were included. Twenty-five of the 84 NT1 patients and all the hypersomnolence disorder patients underwent a follow-up evaluation consisting of clinical assessment, PSG, and a modified MSLT. An additional 68 controls with no sleep disorders were assessed at baseline.

CONCLUSION

Confirming results from previous studies, we found that PSG and our modified MSLT accurately and reliably diagnosed hypocretin-deficient NT1 (accuracy = 0.88, reliability = 0.80). Patients with NT1 had stable clinical and electrophysiological presentations over time that suggested a stable phenotype. In contrast, the PSG/MSLT results of patients with hypersomnolence, and normal CSF-hcrt-1 had poor reliability (0.32) and low repeatability.

Non-invasive detection of narcolepsy type I phenotypical features and disease progression by continuous home-cage monitoring of activity in two mouse models: the HCRT-KO and DTA model

Narcolepsy type 1 (NT1) is a neurological disorder caused by disruption of hypocretin (HCRT; or orexin) neurotransmission leading to fragmented sleep/wake states, excessive daytime sleepiness, and cataplexy (abrupt muscle atonia during wakefulness). Electroencephalography and electromyography (EEG/EMG) monitoring is the gold standard to assess NT1 phenotypical features in both humans and mice. Here, we evaluated the digital ventilated home-cage (DVC®) activity system as an alternative to detect NT1 features in two NT1 mouse models: the genetic HCRT-knockout (-KO) model, and the inducible HCRT neuron-ablation hcrt-tTA;TetO-DTA (DTA) model, including both sexes. NT1 mice exhibited an altered dark phase activity profile and increased state transitions, compared to the wild-type (WT) phenotype. An inability to sustain activity periods >40 min represented a robust activity-based NT1 biomarker. These features were observable within the first weeks of HCRT neuron degeneration in DTA mice. We also created a nest-identification algorithm to differentiate between inactivity and activity, inside and outside the nest as a sleep and wake proxy, respectively, showing significant correlations with EEG/EMG-assessed sleep/wake behavior. Lastly, we tested the sensitivity of the activity system to detect behavioral changes in response to interventions such as repeated saline injection and chocolate. Surprisingly, daily consecutive saline injections significantly reduced activity and increased nest time of HCRT-WT mice. Chocolate increased total activity in all mice, and increased the frequency of short out-of-nest inactivity episodes in HCRT-KO mice. We conclude that the DVC® system provides a useful tool for non-invasive monitoring of NT1 phenotypical features, and has the potential to monitor drug effects in NT1 mice.

Production of human entorhinal stellate cell-like cells by forward programming shows an important role of Foxp1 in reprogramming

Stellate cells are principal neurons in the entorhinal cortex that contribute to spatial processing. They also play a role in the context of Alzheimer's disease as they accumulate Amyloid beta early in the disease. Producing human stellate cells from pluripotent stem cells would allow researchers to study early mechanisms of Alzheimer's disease, however, no protocols currently exist for producing such cells. In order to develop novel stem cell protocols, we characterize at high resolution the development of the porcine medial entorhinal cortex by tracing neuronal and glial subtypes from mid-gestation to the adult brain to identify the transcriptomic profile of progenitor and adult stellate cells. Importantly, we could confirm the robustness of our data by extracting developmental factors from the identified intermediate stellate cell cluster and implemented these factors to generate putative intermediate stellate cells from human induced pluripotent stem cells. Six transcription factors identified from the stellate cell cluster including RUNX1T1, SOX5, FOXP1, MEF2C, TCF4, EYA2 were overexpressed using a forward programming approach to produce neurons expressing a unique combination of RELN, SATB2, LEF1 and BCL11B observed in stellate cells. Further analyses of the individual transcription factors led to the discovery that FOXP1 is critical in the reprogramming process and omission of RUNX1T1 and EYA2 enhances neuron conversion. Our findings contribute not only to the profiling of cell types within the developing and adult brain's medial entorhinal cortex but also provides proof-of-concept for using scRNAseq data to produce entorhinal intermediate stellate cells from human pluripotent stem cells in-vitro.

Sex-related differences within sleep-wake dynamics, cataplexy, and EEG fast-delta power in a narcolepsy mouse model

Narcolepsy type 1 (NT1) is a sleep-wake disorder caused by selective loss of hypocretin (HCRT, also called orexin) neurons. Although the prevalence of NT1 is equal in men and women, sex differences in NT1 symptomatology have been reported in humans and other species. Yet, most preclinical studies fail to include females, resulting in gender bias within translational drug development. We used hcrt-tTA;TetO DTA mice (NT1 mice) that lose their HCRT neurons upon dietary doxycycline removal to examine in detail the effect of sex on NT1 symptoms and sleep-wake characteristics. We recorded 24-h electroencephalography (EEG), electromyography (EMG), and video in adult male and female NT1 mice for behavioural state quantification. While conducting this study, we recognized another type of behavioural arrest different from cataplexy: shorter lasting and with high δ power. We termed these delta attacks and propose a set of criteria for quantifying these in future research. Our findings show that both sexes exhibit high behavioural state instability, which was markedly higher in females with more behavioural arrests interrupting the wake episodes. Females exhibited increased wake at the expense of sleep during the dark phase, and decreased rapid-eye-movement (REM) sleep during the 24-h day. During the dark phase, fast-δ (2.5-4 Hz) in non-rapid-eye-movement (NREM) sleep and θ (6-10 Hz) EEG spectral power in REM sleep were lower in females compared to males. We demonstrate that biologically driven sex-related differences exist in the symptomatology of NT1 mice which calls for including both sexes in future research.

Emerging therapeutic targets for narcolepsy

INTRODUCTION

Narcolepsy type 1 (NT1) and type 2 (NT2) are chronic sleep disorders primarily characterized by excessive daytime sleepiness (EDS), disturbed sleep-wake regulation, and reduced quality of life. The precise disease mechanism is unclear, but it is certain that in NT1 the hypocretin/orexin (Hcrt) system is affected. Current treatment options are symptomatic - they improve EDS and/or reduce cataplexy. Complete symptom control is relatively rare - particularly problematic is residual daytime sleepiness.

AREAS COVERED

This review discusses various emerging treatment targets for narcolepsy. The focus is on the Hcrt receptors but included are also wake-promoting pathways, and sleep-stabilization through GABAergic mechanisms. Additionally, we discuss the potential of targeting the likely autoimmune basis of narcolepsy. PubMed and ClinicalTrials.gov was searched through June 2021 for relevant information.

EXPERT OPINION

Targeting Hcrt receptors has the potential to alleviate narcolepsy symptoms. Results from ongoing drug development programs are promising, but care needs to be taken when evaluating potential side effects. It is still largely unknown what roles Hcrt receptors play in the periphery and how these might be affected by treatment. Immunotherapies could potentially target the core pathophysiology of narcolepsy, but more work is needed to identify the best therapeutic target for this approach.

Diagnostic value of actigraphy in hypersomnolence disorders

OBJECTIVE

Differentiating between the central hypersomnias presents a challenge to the diagnosis of patients with hypersomnolence. Actitigraphy may support efforts to distinguish them. We aimed to evaluate: 1) the ability of actigraphy to quantify sleep continuity measures in comparison with polysomnography in patients with hypersomnolence; 2) whether actigraphy can distinguish patients with hypersomnolence with normal hypocretin-1 in cerebrospinal fluid from patients with narcolepsy type 1 and from sleep-healthy controls; and 3) the distinct activity profiles and circadian rhythms of patients with narcolepsy type 1, patients with hypersomnolence with normal hypocretin-1 in cerebrospinal fluid, and sleep-healthy controls.

METHOD

Polysomnography, multiple sleep latency tests and actigraphy were conducted in 14 patients with narcolepsy type 1, 29 patients with hypersomnolence with normal hypocretin-1 in cerebrospinal fluid and 15 sleep-healthy controls.

RESULTS

Actigraphy quantified several sleep continuity measures consistently with polysomnography in all the patients. Actigraphy distinguished patients with hypersomnolence with normal hypocretin-1 in cerebrospinal fluid from patients with narcolepsy type 1 and sleep-healthy controls. Patients with narcolepsy type 1 had poor sleep quality and altered circadian rest-activity rhythm compared with controls.

CONCLUSION

Actigraphy is an adequate tool for establishing the amount of night sleep and supports the differential diagnosis of patients with hypersomnolence.

GABAA receptor β1 -subunit knock-out mice show increased delta power in NREM sleep and decreased theta power in REM sleep

γ-Aminobutyric acid (GABA) acting through heteropentameric GABA_A receptors plays a pivotal role in the sleep-promoting circuitry. Whereas the role of the different GABA_A receptor α-subunits in sleep regulation and in mediating the effect of benzodiazepines for treatment of insomnia is well-described, the β-subunits are less studied. Here we report the first study characterizing sleep in mice lacking the GABA_A receptor β₁ -subunit (β₁ ^-/- mice). We show that β₁ ^-/- mice have a distinct and abnormal sleep phenotype characterized by increased delta power in non-rapid eye movement (NREM) sleep and decreased theta activity in rapid eye movement (REM) sleep compared to β₁ ^+/+ mice, without any change in the overall sleep-wake architecture. From GABA_A receptor-specific autoradiography, it is further demonstrated that functional β₁ -subunit-containing GABA_A receptors display the highest binding levels in the hippocampus and frontal cortex. In conclusion, this study suggests that the GABA_A receptor β₁ -subunit does not play an important role in sleep initiation or maintenance but instead regulates the power spectrum and especially the expression of theta rhythm. This provides new knowledge on the complex role of GABA_A receptor subunits in sleep regulation. In addition, β₁ ^-/- mice could provide a useful mouse model for future studies of the physiological role of delta and theta rhythms during sleep.

Narcolepsy Type I as an autoimmune disorder

Narcolepsy Type 1 (NT1) is hypothesized to be an autoimmune disease targeting the hypocretin/orexin neurons in the lateral hypothalamus. Ample genetic and epidemiologic evidence point in the direction of a pathogenesis involving the immune system. Many autoantibodies have been detected in blood samples from NT1 patients, but none in a consistent manner. Importantly, T cells directed toward hypocretin/orexin neurons have been detected in samples from NT1 patients. However, it remains to be seen if these potentially autoreactive T cells are also present in the hypothalamus and if they are pathogenic. For this reason, NT1 does still not fully meet the criteria for being classified as a genuine autoimmune disease, even though more and more results are pointing in that direction as will be described in this chapter. The autoimmune hypothesis has led to many attempts at slowing or stopping disease progression with immunomodulatory treatment, but so far the overall results have not been very encouraging. It is clear that more research into the pathogenesis of NT1 is needed to establish the precise role of the immune system in disease development.

Altered surface expression of P2Y11 receptor with narcolepsy-associated mutations

BACKGROUND

Narcolepsy with cataplexy is a neurological sleep disorder, which is believed to arise from the autoimmune destruction of hypocretin-producing neurons. The purinergic receptor P2Y11 is associated with narcolepsy in genome-wide association studies, and P2RY11 sequencing has further revealed eight rare missense mutations associated with the disease. Some of these mutations alter the signaling properties of P2Y11, but for some, no functional effects have been discovered so far.

METHODS

This study examined the surface expression of the eight narcolepsy-associated P2Y11 mutations using an in vitro surface expression assay.

RESULTS

The assay showed excellent discrimination between cells transfected with tagged wild type and the untagged P2Y11 receptor, proving complete specificity towards the 3HA-N-tag used for the assay. Our results show a decreased surface expression of the R307W P2Y11 mutant and a surface expression similar to wild type for the other seven mutants.

CONCLUSION

Based on the present findings, alteration in surface expression is not likely to play a role in how P2Y11 influences narcolepsy pathogenesis. This is important because intact surface expression increases the usefulness of P2Y11 as a future drug target.

CD8+ T cells from patients with narcolepsy and healthy controls recognize hypocretin neuron-specific antigens

Narcolepsy Type 1 (NT1) is a neurological sleep disorder, characterized by the loss of hypocretin/orexin signaling in the brain. Genetic, epidemiological and experimental data support the hypothesis that NT1 is a T-cell-mediated autoimmune disease targeting the hypocretin producing neurons. While autoreactive CD4+ T cells have been detected in patients, CD8+ T cells have only been examined to a minor extent. Here we detect CD8+ T cells specific toward narcolepsy-relevant peptides presented primarily by NT1-associated HLA types in the blood of 20 patients with NT1 as well as in 52 healthy controls, using peptide-MHC-I multimers labeled with DNA barcodes. In healthy controls carrying the disease-predisposing HLA-DQB1*06:02 allele, the frequency of autoreactive CD8+ T cells was lower as compared with both NT1 patients and HLA-DQB1*06:02-negative healthy individuals. These findings suggest that a certain level of CD8+ T-cell reactivity combined with HLA-DQB1*06:02 expression is important for NT1 development.

Type 1 narcolepsy is not present in 29 HPV-vaccinated individuals with subjective sleep complaints

INTRODUCTION

Human papilloma virus (HPV) vaccine uptake in girls and women is dropping markedly in some countries. Concern about the presumed side effects is the commonest reason why. Reports about side effects include specific sleep complaints such as excessive daytime sleepiness, altered dream activity and periods of muscle weakness. These symptoms are commonly seen in individuals with narcolepsy type 1. We aimed to evaluate whether HPV vaccination was associated with the development of hypocretin-deficient narcolepsy.

METHODS

We report the evaluation for sleep disorders, including narcolepsy, in 29 HPV-vaccinated girls and women who were submitted for evaluation of narcolepsy. All were evaluated by polysomnography and the Multiple Sleep Latency Test, and 18 individuals were also evaluated by measures of cerebrospinal fluid hypocretin-1 concentration.

RESULTS

None of the 29 girls and women showed signs of narcolepsy type 1.

CONCLUSION

Our results do not suggest that an association exists between HPV vaccination and the development of narcolepsy type 1.

FUNDING

none.

TRIAL REGISTRATION

not relevant.

DNMT1 regulates expression of MHC class I in post-mitotic neurons

Major Histocompability Complex I (MHC-I) molecules present cellularly derived peptides to the adaptive immune system. Generally MHC-I is not expressed on healthy post-mitotic neurons in the central nervous system, but it is known to increase upon immune activation such as viral infections and also during neurodegenerative processes. MHC-I expression is known to be regulated by the DNA methyltransferase DNMT1 in non-neuronal cells. Interestingly DNMT1 expression is high in neurons despite these being non-dividing. This suggests a role for DNMT1 in neurons beyond the classical re-methylation of DNA after cell division. We thus investigated whether DNMT1 regulates MHC-I in post-mitotic neurons. For this we used primary cultures of mouse cerebellar granule neurons (CGNs). Our results showed that knockdown of DNMT1 in CGNs caused upregulation of some, but not all subtypes of MHC-I genes. This effect was synergistically enhanced by subsequent IFNγ treatment. Overall MHC-I protein level was not affected by knockdown of DNMT1 in CGNs. Instead our results show that the relative MHC-I expression levels among the different MHC subtypes is regulated by DNMT1 activity. In conclusion, we show that while the mouse H2-D1/L alleles are suppressed in neurons by DNMT1 activity under normal circumstances, the H2-K1 allele is not. This finding is particularly important in two instances. One: in the context of CNS autoimmunity with epitope presentation by specific MHC-I subtypes where this allele specific regulation might become important; and two: in amyotropic lateral sclerosis (ALS) where H2-K but not H2-D protects motor neurons from ALS astrocyte-induced toxicity in a mouse model of ALS.

The wake-promoting drug Modafinil prevents motor impairment in sickness behavior induced by LPS in mice: Role for dopaminergic D1 receptor

The wake-promoting drug Modafinil has been used for many years for treatment of Narcolepsy and Excessive Daytime Sleepiness, due to a dopamine-related psychostimulant action. Recent studies have indicated that Modafinil prevents neuroinflammation in animal models. Thus, the aim of the present study was to evaluate the effect of Modafinil pretreatment in the Lipopolysaccharide (LPS)-induced sickness and depressive-like behaviors. Adult male C57BL/6J mice were pretreated with Vehicle or Modafinil (90mg/Kg) and, 30min later, received a single saline or LPS (2mg/Kg) administration, and were submitted to the open field and elevated plus maze test 2h later. After 24h, mice were subjected to tail suspension test, followed by either flow cytometry with whole brain for CD11b⁺CD45⁺ cells or qPCR in brain areas for cytokine gene expression. Modafinil treatment prevented the LPS-induced motor impairment, anxiety-like and depressive-like behaviors, as well as the increase in brain CD11b⁺CD45^high cells induced by LPS. Our results indicate that Modafinil pretreatment also decreased the IL-1β gene upregulation caused by LPS in brain areas, which is possibly correlated with the preventive behavioral effects. The pharmacological blockage of the dopaminergic D1R by the drug SCH-23390 counteracted the effect of Modafinil on locomotion and anxiety-like behavior, but not on depressive-like behavior and brain immune cells. The dopaminergic D1 receptor signaling is essential to the Modafinil effects on LPS-induced alterations in locomotion and anxiety, but not on depression and brain macrophages. This evidence suggests that Modafinil treatment might be useful to prevent inflammation-related behavioral alterations, possibly due to a neuroimmune mechanism.

Increased interferon-mediated immunity following in vitro and in vivo Modafinil treatment on peripheral immune cells

The wake-promoting drug Modafinil has been used for treatment of sleep disorders, such as Narcolepsy, excessive daytime sleepiness and sleep apnea, due to its stimulant action. Despite the known effect of Modafinil on brain neurochemistry, particularly on brain dopamine system, recent evidence support an immunomodulatory role for Modafinil treatment in neuroinflammatory models. Here, we aimed to study the effects of in vitro and in vivo Modafinil treatment on activation, proliferation, cell viability, and cytokine production by immune cells in splenocytes culture from mice. The results show that in vitro treatment with Modafinil increased Interferon (IFN)-γ, Interleukin (IL)-2 and IL-17 production and CD25 expression by T cells. In turn, in vivo Modafinil treatment enhanced splenocyte production of IFN-γ, IL-6 and tumor necrosis factor (TNF), and increased the number of IFN-γ producing cells. Next, we addressed the translational value of the observed effects by testing PBMCs from Narcolepsy type 1 patients that underwent Modafinil treatment. We reported increased number of IFN-γ producing cells in PBMCs from Narcolepsy type 1 patients following continuous Modafinil treatment, corroborating our animal data. Taken together, our results show, for the first time, a pro-inflammatory action of Modafinil, particularly on IFN-mediated immunity, in mice and in patients with Narcolepsy type 1. The study suggests a novel effect of this drug treatment, which should be taken into consideration when given concomitantly with an ongoing inflammatory or autoimmune process.

N-terminal tagging of human P2X7 receptor disturbs calcium influx and dye uptake

The P2X7 receptor is a frequently studied member of the purinergic receptor family signalling via channel opening and membrane pore formation. Fluorescent imaging is an important molecular method for studying cellular receptor expression and localization. Fusion of receptors to fluorescent proteins might cause major functional changes and requires careful functional evaluation such as has been done for the rat P2X7 receptor. This study examines fusion constructs of the human P2X7 receptor. We assessed surface expression, channel opening with calcium influx, and pore formation using YO-PRO-1 dye uptake in response to BzATP stimulation in transfected cells. We found that tagging at the N-terminal of the human P2X7 receptor with the enhanced green fluorescent protein (eGFP) disturbed channel opening and pore formation despite intact surface expression. A triple hemagglutinin (3HA) fused to the N-terminal also disrupted pore formation but not channel opening showing that even a small tag alters the normal function of the receptor. Together, this suggests that in contrast to what has been observed for the rat P2X7 receptor, the human P2X7 receptor contains N-terminal motifs important for signalling that prevent the construction of a functionally active fusion protein.

Cerebrospinal Fluid Biomarkers of Neurodegeneration Are Decreased or Normal in Narcolepsy

Objectives

To investigate whether cerebrospinal fluid (CSF) biomarkers of neurodegeneration are altered in narcolepsy in order to evaluate whether the hypocretin deficiency and abnormal sleep-wake pattern in narcolepsy leads to neurodegeneration.

Methods

Twenty-one patients with central hypersomnia (10 type 1 narcolepsy, 5 type 2 narcolepsy, and 6 idiopathic hypersomnia cases), aged 33 years on average and with a disease duration of 2-29 years, and 12 healthy controls underwent CSF analyses of the levels of β-amyloid, total tau protein (T-tau), phosphorylated tau protein (P-tau181), α-synuclein, neurofilament light chain (NF-L), and chitinase 3-like protein-1 (CHI3L1).

Results

Levels of β-amyloid were lower in patients with type 1 narcolepsy (375.4 ± 143.5 pg/mL) and type 2 narcolepsy (455.9 ± 65.0 pg/mL) compared to controls (697.9 ± 167.3 pg/mL, p < .05). Furthermore, in patients with type 1 narcolepsy, levels of T-tau (79.0 ± 27.5 pg/mL) and P-tau181 (19.1 ± 4.3 pg/mL) were lower than in controls (162.2 ± 49.9 pg/mL and 33.8 ± 9.2 pg/mL, p < .05). Levels of α-synuclein, NF-L, and CHI3L1 in CSF from narcolepsy patients were similar to those of healthy individuals.

Conclusion

Six CSF biomarkers of neurodegeneration were decreased or normal in narcolepsy indicating that taupathy, synucleinopathy, and immunopathy are not prevalent in narcolepsy patients with a disease duration of 2-29 years. Lower CSF levels of β-amyloid, T-tau protein, and P-tau181 in narcolepsy may indicate that hypocretin deficiency and an abnormal sleep-wake pattern alter the turnover of these proteins in the central nervous system.

Neurobasal media facilitates increased specificity of siRNA-mediated knockdown in primary cerebellar cultures

BACKGROUND

Efficient and specific knockdown of proteins in post-mitotic cells such as differentiated neurons can be difficult to achieve. Further, special care must be taken to maintain the health of neurons in vitro. We wanted to achieve knockdown in primary cerebellar granule neurons, which can be effectively grown in Neurobasal™ media.

NEW METHOD

We tested the efficiency of siRNA from the Accell range from Dharmacon™ when delivered in Neurobasal™ media in contrast to the recommended Accell Delivery media provided by the manufacturer.

RESULTS

We observed a more specific knockdown of target in Neurobasal™ media, than in Accell Delivery media when using cerebellar granule neurons. Transfection efficiency and cell viability was comparable between the two media.

COMPARISON WITH EXISTING METHODS

Delivery of siRNA in Neurobasal™ media facilitates increased specificity of the knockdown compared to delivery in Accell Delivery media. The off-target effect observed in Accell Delivery media was not a secondary biological response to downregulation of target, but rather a mixture of specific and non-specific off-target effects.

CONCLUSIONS

Specific knockdown of target can be achieved in primary cerebellar granule cells using Accell siRNAs in Neurobasal™ media. This method ensures specific knockdown in post-mitotic neurons without the need for biosafety level 2 laboratories, additional reagents, or instruments needed by other transfection.

Validation of antibodies for neuroanatomical localization of the P2Y11 receptor in macaque brain

Focus on the purinergic receptor P2Y₁₁ has increased following the finding of an association between the sleep disorder narcolepsy and a genetic variant in P2RY11 causing decreased gene expression. Narcolepsy is believed to arise from an autoimmune destruction of the hypothalamic neurons that produce the neuropeptide hypocretin/orexin. It is unknown how a decrease in expression of P2Y₁₁ might contribute to an autoimmune reaction towards the hypocretin neurons and the development of narcolepsy. To advance narcolepsy research it is therefore extremely important to determine the neuroanatomical localization of P2Y₁₁ in the brain with particular emphasis on the hypocretin neurons. In this article we used western blot, staining of blood smears, and flow cytometry to select two antibodies for immunohistochemical staining of macaque monkey brain. Staining was seen in neuron-like structures in cortical and hypothalamic regions. Rats do not have a gene orthologue to the P2Y₁₁ receptor and therefore rat brain was used as negative control tissue. The chromogenic signal observed in macaque monkey brain in neurons was not considered reliable, because the antibodies stained rat brain in a similar distribution pattern. Hence, the neuroanatomical localization of the P2Y₁₁ receptor remains undetermined due to the lack of specific P2Y₁₁ antibodies for brain immunohistochemistry.

A critical look at the function of the P2Y11 receptor

The P2Y11 receptor is a member of the purinergic receptor family. It has been overlooked, somewhat due to the lack of a P2ry11 gene orthologue in the murine genome, which prevents the generation of knockout mice, which have been so helpful for defining the roles of other P2Y receptors. Furthermore, some of the studies reported to date have methodological shortcomings, making it difficult to determine the function of P2Y11 with certainty. In this review, we discuss the lack of a murine "P2Y11-like receptor" and highlight the limitations of the currently available methods used to investigate the P2Y11 receptor. These methods include protein recognition with antibodies that show very little specificity, gene expression studies that completely overlook the existence of a fusion transcript between the adjacent PPAN gene and P2RY11, and agonists/antagonists reported to be specific for the P2Y11 receptor but which have not been tested for activity on numerous other adenosine 5'-triphosphate (ATP)-binding receptors. We suggest a set of criteria for evaluating whether a dataset describes effects mediated by the P2Y11 receptor. Following these criteria, we conclude that the current evidence suggests a role for P2Y11 in immune activation with cell type-specific effects.

Cerebrospinal Fluid Hypocretin-1 (Orexin-A) Level Fluctuates with Season and Correlates with Day Length

The hypocretin/orexin neuropeptides (hcrt) are key players in the control of sleep and wakefulness evidenced by the fact that lack of hcrt leads to the sleep disorder Narcolepsy Type 1. Sleep disturbances are common in mood disorders, and hcrt has been suggested to be poorly regulated in depressed subjects. To study seasonal variation in hcrt levels, we obtained data on hcrt-1 levels in the cerebrospinal fluid (CSF) from 227 human individuals evaluated for central hypersomnias at a Danish sleep center. The samples were taken over a 4 year timespan, and obtained in the morning hours, thus avoiding impact of the diurnal hcrt variation. Hcrt-1 concentration was determined in a standardized radioimmunoassay. Using biometric data and sleep parameters, a multivariate regression analysis was performed. We found that the average monthly CSF hcrt-1 levels varied significantly across the seasons following a sine wave with its peak in the summer (June-July). The amplitude was 19.9 pg hcrt/mL [12.8-26.9] corresponding to a 10.6% increase in midsummer compared to winter. Factors found to significantly predict the hcrt-1 values were day length, presence of snow, and proximity to the Christmas holiday season. The hcrt-1 values from January were much higher than predicted from the model, suggestive of additional factors influencing the CSF hcrt-1 levels such as social interaction. This study provides evidence that human CSF hcrt-1 levels vary with season, correlating with day length. This finding could have implications for the understanding of winter tiredness, fatigue, and seasonal affective disorder. This is the first time a seasonal variation of hcrt-1 levels has been shown, demonstrating that the hcrt system is, like other neurotransmitter systems, subjected to long term modulation.

Cerebrospinal fluid cytokine levels in type 1 narcolepsy patients very close to onset

Type 1 narcolepsy is caused by a loss of hypocretin (orexin) signaling in the brain. Genetic data suggests the disorder is caused by an autoimmune attack on hypocretin producing neurons in hypothalamus. This hypothesis has however not yet been confirmed by consistent findings of autoreactive antibodies or T-cells in patient samples. One explanation for these negative results may be that the autoimmune process is no longer active when patients present to the clinic. With increasing awareness in recent years, more and more patients have been diagnosed closer and closer to disease onset. In this study, we tested whether an active immune process in the brain could be detected in these patients, as reflected by increased cytokine levels in the cerebrospinal fluid (CSF). Using multiplex analysis, we measured the levels of 51 cytokines and chemokines in the CSF of 40 type 1 narcolepsy patients having varying disease duration. For comparison, we used samples from 9 healthy controls and 9 patients with other central hypersomnia. Cytokine levels did not differ significantly between controls and patients, even in 5 patients with disease onset less than a month prior to CSF sampling.

Type 1 narcolepsy: a CD8(+) T cell-mediated disease?

Type 1 narcolepsy is a sleep disorder characterized by excessive daytime sleepiness with unintentional sleep attacks and cataplexy. The disorder is caused by a loss of hypocretinergic neurons in the brain. The specific loss of these neurons in narcolepsy is thought to result from an autoimmune attack, and this is supported by evidence of both environmental and genetic factors pointing toward an involvement of the immune system. However, definitive proof of an autoimmune etiology is still missing. Several different immune-mediated disorders targeting neurons are known, and many of these are believed to be caused by autoreactive CD8(+) T cells. In this paper, we review the current knowledge on CD8(+) T cell-mediated neuronal damage on the basis of our understanding of other autoimmune disorders and experimental studies. We identify major histocompatibility complex class I presentation of autoantigens on neurons as a possible mechanism in the development of the disease, and propose T cell-mediated pathogenesis, with cytotoxic CD8(+) T cells targeting the hypocretinergic neurons, as a central element.

CD4+ T cell autoimmunity to hypocretin/orexin and cross-reactivity to a 2009 H1N1 influenza A epitope in narcolepsy

Narcolepsy, a disorder strongly associated with human leukocyte antigen (HLA)-DQA1*01:02/DQB1*06:02 (DQ0602), is characterized by excessive daytime sleepiness, cataplexy, and rapid eye movement sleep abnormalities. It is caused by the loss of ~70,000 posterior hypothalamic neurons that produce the wake-promoting neuropeptide hypocretin (HCRT) (orexin). We identified two DQ0602-binding HCRT epitopes, HCRT56-68 and HCRT87-99, that activated a subpopulation of CD4(+) T cells in narcolepsy patients but not in DQ0602-positive healthy control subjects. Because of the established association of narcolepsy with the 2009 H1N1 influenza A strain (pH1N1), we administered a seasonal influenza vaccine (containing pH1N1) to patients with narcolepsy and found an increased frequency of circulating HCRT56-68- and HCRT87-99-reactive T cells. We also identified a hemagglutinin (HA) pHA1 epitope specific to the 2009 H1N1 strain, pHA1275-287, with homology to HCRT56-68 and HCRT87-99. In vitro stimulation of narcolepsy CD4(+) T cells with pH1N1 proteins or pHA1275-287 increased the frequency of HCRT56-68- and HCRT87-99-reactive T cells. Our data indicate the presence of CD4(+) T cells that are reactive to HCRT in narcolepsy patients and possible molecular mimicry between HCRT and a similar epitope in influenza pH1N1, pHA1275-287.

Narcolepsy as an autoimmune disease: the role of H1N1 infection and vaccination

Narcolepsy is a sleep disorder characterised by loss of hypothalamic hypocretin (orexin) neurons. The prevalence of narcolepsy is about 30 per 100 000 people, and typical age at onset is 12-16 years. Narcolepsy is strongly associated with the HLA-DQB1*06:02 genotype, and has been thought of as an immune-mediated disease. Other risk genes, such as T-cell-receptor α chain and purinergic receptor subtype 2Y11, are also implicated. Interest in narcolepsy has increased since the epidemiological observations that H1N1 infection and vaccination are potential triggering factors, and an increase in the incidence of narcolepsy after the pandemic AS03 adjuvanted H1N1 vaccination in 2010 from Sweden and Finland supports the immune-mediated pathogenesis. Epidemiological observations from studies in China also suggest a role for H1N1 virus infections as a trigger for narcolepsy. Although the pathological mechanisms are unknown, an H1N1 virus-derived antigen might be the trigger.

ImmunoChip study implicates antigen presentation to T cells in narcolepsy

Recent advances in the identification of susceptibility genes and environmental exposures provide broad support for a post-infectious autoimmune basis for narcolepsy/hypocretin (orexin) deficiency. We genotyped loci associated with other autoimmune and inflammatory diseases in 1,886 individuals with hypocretin-deficient narcolepsy and 10,421 controls, all of European ancestry, using a custom genotyping array (ImmunoChip). Three loci located outside the Human Leukocyte Antigen (HLA) region on chromosome 6 were significantly associated with disease risk. In addition to a strong signal in the T cell receptor alpha (TRA@), variants in two additional narcolepsy loci, Cathepsin H (CTSH) and Tumor necrosis factor (ligand) superfamily member 4 (TNFSF4, also called OX40L), attained genome-wide significance. These findings underline the importance of antigen presentation by HLA Class II to T cells in the pathophysiology of this autoimmune disease.

While there is now broad consensus that narcolepsy-hypocretin deficiency results from a highly specific autoimmune attack on hypocretin cells, little is understood regarding the initiation and progression of the underlying autoimmune process. We have taken advantage of a unique high-density genotyping platform (the ImmunoChip) designed to study variants in genes known to be important to autoimmune and inflammatory diseases. Our study of nearly 2000 narcolepsy cases compared to 10,000 controls underscored important roles for HLA DQB1*06:02 and the T cell receptor alpha genes and implicated two additional genes, Cathepsin H and TNFSF4/OX40L, in disease pathogenesis. These findings are particularly important, as these encoded proteins have key roles in antigen processing, presentation, and T cell response, and they suggest that specific interactions at the immunological synapse constitute the pathway to the disease. Further studies of these genes and encoded proteins may therefore reveal the mechanism leading to this highly selective and unique autoimmune disease.

DQB1*06:02 allele-specific expression varies by allelic dosage, not narcolepsy status

The association of narcolepsy-cataplexy, a sleep disorder caused by the loss of hypocretin/orexin neurons in the hypothalamus, with DQA1*01:02-DQB1*06:02 is one of the tightest known single-allele human leukocyte antigen (HLA) associations. In this study, we explored genome-wide expression in peripheral white blood cells of 50 narcolepsy versus 47 controls (half of whom were DQB1*06:02 positive) and observed the largest differences between the groups in the signal from HLA probes. Further studies of HLA-DQ expression (mRNA and protein in a subset) in 125 controls and 147 narcolepsy cases did not reveal any difference, a result we explain by the lack of proper control of allelic diversity in Affymetrix HLA probes. Rather, a clear effect of DQB1*06:02 allelic dosage on DQB1*06:02 mRNA levels (1.65-fold) and protein (1.59-fold) could be demonstrated independent of disease status. These results indicate that allelic dosage is transmitted into changes in heterodimer availability, a phenomenon that may explain the increased risk for narcolepsy in DQB1*06:02 homozygotes versus heterozygotes.

Central serotonin depletion affects rat brain areas differently: a qualitative and quantitative comparison between different treatment schemes

Depletion of rat brain serotonin (5-hydroxytryptamin, 5-HT) has been widely used to study effects of serotonin and its interaction with other transmitter systems. Various treatment regimes for serotonin depletion have been applied, but the efficacy of these seems to vary considerably. So far, no studies have systematically examined and compared different approaches. The present work combines quantitative and qualitative measurements and compares six different treatment schemes for 5-HT depletion. Treatment outcome was evaluated by HPLC measurements of 5-HT and 5-HIAA concentrations, and by 5-HT and tyrosine hydroxylase immunocytochemistry. The schemes included repeated administration of fenfluramine (FEN) and/or p-chlorophenylalanine (pCPA). The most efficient treatment for rat brain 5-HT depletion was the combined treatment with one daily pCPA (200 mg/kg) injection for 3 days followed by one injection of d,l-FEN (20 mg/kg) on the fourth day, causing a 94.9% brain 5-HT depletion. Immunostaining revealed a distinct brain distribution of the remaining 5-HT, with an almost complete depletion of 5-HT in the cerebral cortex, hippocampus and thalamus, while a substantial amount of 5-HT still was left in the raphe nuclei, the medial forebrain bundle, and the medial eminence. FEN or pCPA treatment alone caused from 68.2 to 94.0% decrease in 5-HT levels. While the pattern of 5-HT depletion using pCPA alone was comparable to the one seen with the combined treatment, the 5-HT depletion using FEN alone showed a different pattern with 5-HT distributed in several brain regions.